Purpose: This study evaluates the effects of the essential oils Origanum vulgare L. (OVEO) and Rosmarinus officinalis L. (ROEO) and their major constituents carvacrol (CAR) and 1,8-cineole (CIN) applied in combination, against a cocktail of five S. aureus strains in cheese and meat-based models.
Methods: Samples (10 g) of semi-hard cheese or ground beef were mixed with OVEO+ROEO or CAR+CIN at the Fractional Inhibitory Concentration (FIC), where FIC is typically the Minimum Inhibitory Concentration (MIC)/4. These mixtures were inoculated with 1 ml of bacterial suspension (107 CFU/ml), blended for 5 min and incubated at 8 - 10°C. Systems without antimicrobials were assayed similarly. The viable cells were enumerated at various time points (0, 24, 48 and 72 h) by serial dilution and plating on Brain Heart Infusion agar with sodium chloride 8.5%
Results: The cheese and meat systems with OVEO+ROEO showed reductions of 1.8 log CFU/g and 1.6 log CFU/g, respectively, after 48 h; when CAR+CIN were used, reduction of 1.9 CFU/g and 1.7 CFU/g were observed for cheese and meat systems, respectively. Cheese and meat model systems containing essential oils or constituents at showed greater than a 2.8-log reduction in S. aureus counts after 72 h. Control experiments for both matrices without added antimicrobials showed no change in S. aureus concentration over 72 h.
Significance: The essential oils OVEO and ROEO and their major constituents CAR and CIN, are effective in combination in controlling multiple S. aureus strains in cheese and meat-based models. These results support the idea that the combination of these substances could be used to control the growth and survival of S. aureus in food.